During the morphogenesis of animal and bacterial DNA viruses DNA is packaged in a protein envelope. Our long-range objective is to understand the mechanism of virus DNA packaging at the molecular level. To reach this goal we will use bacteriophage T7 as a model system and will pursue the following short-range objectives: a) isolation from T7-infected E. coli of supramolecular intermediates in the DNA packaging pathway, and b) characterization of isolated intermediates using physical and chemical techniques. Mutational alteration of the DNA packaging pathway will be used to help isolate intermediates that are transient or unstable during normal infections. To determine the order of occurrence of intermediates in the DNA packaging pathway we will determine their kinetics of appearance and will determine which intermediates are assembled by T7 amber mutants in a non-permissive host. Techniques used to isolate and characterize intermediates include: electrophoresis under non-denaturing conditions, velocity and buoyant density ultracentrifugation, and electron microscopy. Attempts will be made to improve existing techniques for isolating and characterizing supramolecular complexes of DNA and protein. Ultimately we will develop dynamic models for the DNA packaging process from the above data. To test models we will attempt to have purified intermediates re-enter the DNA packaging pathway in cell-free mixtures under controlled conditions.